Disable pip cache during docker build

Ref #188

(c) Copyright IBM Corp. 2016

all-spark-notebook/Dockerfile

@@ -28,5 +28,5 @@ RUN conda config --add channels r && \
     'r-rcurl=1.95*' && conda clean -tipsy
 
 # Apache Toree kernel
-RUN pip install toree==0.1.0.dev7
+RUN pip --no-cache-dir install toree==0.1.0.dev7
 RUN jupyter toree install --user

base-notebook/Dockerfile

@@ -69,7 +69,7 @@ RUN conda install --quiet --yes \
     && conda clean -tipsy
 
 # Install JupyterHub to get the jupyterhub-singleuser startup script
-RUN pip install 'jupyterhub==0.5'
+RUN pip --no-cache-dir install 'jupyterhub==0.5'
 
 USER root